History of Diversity Reception
- Diversity receiving equipment utilizes two or more
receivers connected together at the second detectors and AVC lines. The receiver
inputs are from widely separated antennas. The goal of a diversity receiver is
to greatly reduce
or eliminate fading radio signals. Fading radio signals have always plagued
shortwave reception and are encountered when the signals
being received originate from a transmitting station located at a distance that requires
the radio waves to propagate via skywave through the ionosphere. As signals fade down to the noise
level much of the information being transmitted is lost until the signal level increases
above the noise again. Sometimes deep fades will last for half a minute or more,
causing program interruption or important messages to be lost. Besides fading,
other phenomena occurs
when radio waves are refracted through the ionosphere, such as selective
sideband fading causing distortion on AM signals along with rotation of the
radio waves causing polarization changes.

In the early 1920s, two engineers working for RCA, Harold
H.
Beverage and H.O. Peterson, began investigating what was actually happening when
signals faded. The event that fomented Beverage and Peterson's
interest happened when the two were monitoring signal reception
from two points simultaneously. They were utilizing a telephone
line to monitor Peterson's receiver at his home and were
comparing that to the received signals from the RCA station
site, located about one-half mile away. By monitoring the same
transmitter signal as received from two different locations
simultaneously, Beverage and Peterson noted that each station
received the signal with different fading characteristics. More
tests showed that different fading occurred with as little as
three hundred feet of separation of the receiving antennas.

Beverage and Peterson first
connected strip-chart recorders to a combination of three antennas and
three receivers. The charts showed that not only was the same signal at
different amplitudes at each antenna but, at any one instant, the signal
at one antenna was also many times out of phase with that same signal on
the other antennas. At first the engineers speculated that radio waves
were being refracted in the ionosphere at different angles and therefore
some waves would be intercepted by an antenna while other wave-angles
would miss the antenna. A large multiple antenna should capture more
wave angles and reduce fading. Actually, they found the opposite
happened. Fading became worse with larger antenna arrays. The two men
then theorized that over-the-horizon radio waves could be refracted
simultaneously from different heights in the ionosphere, these waves
would travel slightly longer or shorter paths and arrive at a single
antenna at slightly different times. The delay of the longer path
signals would sometimes cause multiple phases of the signal to occur on
a single antenna. Sometimes the phase differences would add resulting in
stronger signals and sometimes the phases would cancel causing a drop in
signal strength. Since the ionosphere was nearly always in a changing
state and since radio waves would frequently be simultaneously refracted
at several different levels in the ionosphere, fading due to radio wave
phase changes on a single antenna was always going to be present.

The solution was to use
separate antennas and separate receivers to provide the
isolation necessary so each antenna and receiver would react to
radio waves specific to its time and space relationship. As the
signals passed through the receivers, the various phases at the
RF frequency maintained their out of phase relationship until
they were converted to audio signals at the second detector. The
process of detection eliminated the RF out of phase nature of
the signals since now the signal information was at an audio
frequency. Each second detector output would be tied together
with a common load, operating an AVC system that interconnected
all the receivers, resulting in a single audio signal the
amplitude of which was the result of the strongest received
signal at any one time. Through experimentation, it was found
that at least a full wavelength of antenna separation was
necessary to have consistent difference in the phase of the
signals.

Additional problems started to surface when it became necessary
for the diversity receivers to operate on CW. The interaction of the receivers in
maintaining a constant detector load output regardless of variations on the separate antenna-receiver
inputs required the AVC to be operational. When a BFO was injected into the second
detectors the strength of the BFO oscillator would capture the AVC and not allow
it to follow the signal strength variations in that receiver. >>>

>>> The solution was to either send
modulated CW from the transmitting station, which wasn't always practical, or the second
detector outputs could be used (without a BFO) to operate an external device called a Tone
Keyer. The Tone Keyer provided a clean CW output that was devoid of any noise, static or
interference since it was "keyed" from the diversity output of the detectors.
This then allowed the system AVC to be in operation and standard CW to be received. Beverage and Peterson, while working at Riverhead, NY, installed
the first space diversity stations for reliable, long-distance communication.

By the late
twenties, RCA had 41 triple-diversity receivers installed at Riverhead in communications
with 26 different countries. The outputs were routed to a main office in New York City
where operators would copy the strip tapes, decoding the messages. By using filters and
multiple tones, several signals could be routed simultaneously to the main office without
interference. The associated antenna farm, with 1000 feet of separation between antennas,
required acres of land. The installation was used for commercial sending and receiving
world-wide radiograms.

As receiver design progressed, the diversity stations became more
sophisticated. By the forties, RCA had introduced its AR-88 receiver which was adapted to
the new triple-diversity receiver, the DR-89 (Navy designation RDM.) These seven foot tall racks contained three
AR-88 receivers, a Tone Keyer with combined output meter, a Speaker Panel, a Meter Panel
with S-meters for all three receivers, an antenna patch panel and a power supply. Even more
complex was the military RCP and RBP-1, also built by RCA for the Navy during
WWII. The RCP used double conversion receivers with multiple tuners installed in four, seven foot
tall racks. The RBP-1 was a dual-triple diversity receiver that was essentially two
RCPs
side-by-side. Using six double conversion receivers in seven racks the entire setup
weighed a mere one and a half tons! The RBP-1s were still in use as late as the 1970s.

The Signal Corps also used
diversity in many of their teletype installations. The system used was
"frequency diversity" which used one frequency and receiver for "mark" and
another frequency and receiver for "space." The theory was that each frequency
would fade differently and rarely would both frequencies fade together. Only
either a mark or a space was needed to decode the teletype, (if it isn't a mark
- it must be a space.) The popular receivers used were the Collins R-388, R-390
and the R-390A.

Another form of diversity
was to use a vertical oriented antenna in combination with a horizontal
antenna. The theory was that the radio waves many times rotated as they were
refracted through the ionosphere and therefore good diversity action could
be achieved with both vertical and horizontal polarization. This form was
called "polar diversity" and was generally used when a full wavelength of
antenna separation wasn't practical. In the early forties, a QST article featured a novel way to
experience a diversity action using only a single receiver. The writer used a high speed
antenna switch, running at 400Hz, to switch between two antennas. The average of the
signal strength of each antenna was more or less what the receiver responded to supposedly
giving some relief to fading. Additionally, the 400Hz switching gave a sort of modulation
to the signals so CW was easy to copy without a BFO.

Amateur interest in diversity reception waned as WWII loomed in
the near future. The expense, the complexity, the space required for antennas all made the
results not worth the effort. With less expensive equipment most hams could get the same
results. So what if the 'phone stations needed to repeat some of their transmission. On
CW, there was no obvious benefit to diversity and, in the pre-WWII days, most hams were on
CW. After WWII, there is hardly any mention of diversity in any ham magazines.
The commercial stations and the military had always been and were to remain the
primary users of diversity reception. As technology progressed into satellite
communications by the late 70s and other more reliable forms of communication
came into use, the need for large, expensive diversity receiving installations
all but vanished. Most of the equipment has been scraped or sold into surplus.

Development of the Skyrider Diversity

Amateurs became familiar with the principals of diversity
reception by reading various books and magazine articles throughout the twenties and
thirties. QST published an article by Chester W. Rice in the August 1927 issue about shortwave
uses that mentioned diversity theory and reception. For the avid 'phone operator, having
the equipment to eliminate fading signals and the associated distortion, must have seemed
like a virtual necessity. To the CW op though, diversity seemed to not be worth the
effort, after all, CW copy was not that seriously affected by fading. However, James Lamb, Technical Editor for QST, and engineer James McLaughlin decided that diversity was worth a try and began their
research into some kind of practical amateur receiver that would incorporate diversity.

The XE1G Receiver - The First
Amateur Dual Diversity Receiver

James Lamb and James McLaughlin had been experimenting with
diversity reception as early as 1931. At that time, the two engineers used two shortwave
converters connected to two identical TRF receivers used as IF amplifiers. Both TRF
receivers had been modified to have amplified AVC. The performance was satisfactory enough
for each to continue their research and designs. For the next few years, each pursued
their own careers but decided to have an informal meeting in the spring of 1935. The
purpose of the meeting was to discuss each others thoughts on what technical advances
might be used to create a practical amateur diversity receiver. At about the same time, well-known
amateur operator Dr. James M. B. Hard, XE1G from Cuernavaca, Morelos, Mexico, let it
be known he was ready to finance the construction of a dual-diversity receiver of Lamb's
and McLaughlin's design.

Both Lamb and McLaughlin thought that the tuning of commercial
diversity receivers was too cumbersome. In commercial installations, where usually only a
few frequencies were used, tuning each of the receivers to a specific frequency was a task
only performed once or twice a day. In an amateur station, the ability to tune though each
amateur band easily and switch from band to band quickly was an obvious necessity. The
XE1G receiver uses a single Local Oscillator between the two receiver front-ends to
provide "single dial" tuning. Other circuits incorporated in the XE1G receiver
were chain-drive for the band switch, separate pre-selector tuning (not ganged to the main
tuning,) three power supplies, separate audio amplifier using a modified Collins 7C audio
amplifier, tuning coverage from 1.7MC to 30MC in four tuning ranges, amplified AVC and a
separate Jensen speaker with an add-on tweeter unit. The completed receiver was delivered
to Dr. Hard in the Spring of 1936.

Photo left shows the XE1G receiver as it appeared in the May 1936
issue of QST along with an article describing the receiver in detail. The rack contains
the dual receivers, pre-selectors and multiple power supplies. Shown on top of the speaker
is the modified Collins 7C audio amplifier. The speaker cabinet contains a Jensen speaker
with an add-on tweeter unit.

XE1G - Dr. James M. B. Hard

To the left is a 1937 photo of Dr. James M. B. Hard at his station, XE1G.
Note that the Lamb-McLaughlin Diversity Receiver is in the front-left side of the
station along with the Collins audio amplifier and the Jensen speaker. It also appears to have been repainted when compared to the QST
photo of 1936.

XE1G was an incredible station as can be seen from the photo.
Other equipment included an RME-69 receiver with Peak Preselector, a Hammarlund
Super-Pro receiver (against the wall, far right,) an oscilloscope and frequency meter are on the right
side of the operating position table and to the right of the clock is a variac. A 1KW transmitter
is against the wall left and a 100W
transmitter against the wall right. The antenna feed lines drop through
glass plates in the ceiling. Between the two transmitters are large
meters that monitored the voltage and current coming into the shack. Dr. Hard had a private 3000vac line
running one half mile from the power company main line to a pole
transformer on his property. The HV line was stepped down to 240vac and
then run underground some 800 feet to his hacienda. All lines in the
house were
run in iron conduit that was embedded in the concrete floors. The shack
earth-grounds consisted of 2" copper ribbon buried under the foundation of the
building. The XE1G antenna was supported by three 160 foot masts. Using
a system of weights and pulleys any of the radiating systems could be
raised or lowered or even tilted at angles as much as 45 degrees. XE1G was a famous amateur station in the mid to late 1930s and
Dr. Hard worked the world from his QTH in Morelos, Mexico.

photo: Dr. James M. B.
Hard, XE1G, in his station. May 1937 "RADIO" magazine published
in Los Angeles, California. Dr. Hard's Custom Diversity Receiver is
dominate in the left foreground of the photo.

The First Prototype DD-1

The Prototype DD-1 built by James McLaughlin and
Karl Miles in 1937

Photo QST, Dec. 1937

Shortly after the QST article about the XE1G receiver was
published, Hallicrafters became interested in building a Dual Diversity receiver
for the amateur market. Karl W. Miles, Hallicrafters' chief engineer, was given the task of developing the
working prototype. Working directly with James McLaughlin, Karl Miles was to build a dual
diversity receiver, based on the XE1G receiver, that was within the capabilities
of the company to manufacture.

The first prototype was given ample space in the December, 1937 issue of QST. The simplified schematic shows that the prototype now has the preselector stage ganged to the second RF and Mixer stages. The Diversity Meters are now
in a small cabinet that can be placed near the receiver. The Infinite-Rejection system is
now incorporated into the IF amplifier. Separate Power Supply and Amplifier are now in
much smaller cases which can be placed on each side of the receiver but they are not shown
in the schematic. Obvious in the photo of the prototype are the many Hallicrafters parts
utilized in the construction.

By the time McLaughlin and Miles started work on their
new prototype, the XE1G receiver had logged in 5000 hours of reliable operation.
Dr. Hard was still enthusiastic about his receiver and stated that many times,
with poor conditions, only it could be relied upon for intelligible reception.
He mainly operated on 20 meters with two antennas spaced at 50 feet, not the
ideal spacing but sufficient to provide usable diversity action. With
improvements that had been developed since mid-1936, mainly in mechanical
design, IF amplifier improvements and the Infinite-Rejection system, Miles' and
McLaughlin's new version would cover .54 to 36 MC in five bands, have a simpler band switch system and be
housed in a smaller cabinet. The article concluded with a rather vague
statement about how the audio modulation for CW is not really working satisfactory and
there were still "bugs" to be worked out. >>>

>>> This earliest prototype is very different from the
later prototype and the production DD-1. Some of the more obvious changes for the Hallicrafters production units included
changing the rotary bandswitch to
the massive push-button band switch assembly built by Mallory-Yaxley. The top button is the
power switch while the remaining six buttons select the bands. Frequency coverage was also
changed from the early prototype with the new range being .54MC to 45MC in six bands. With this
new higher frequency, the old 6K7 RF amplifiers were changed to the new Raytheon VHF
amplifier tube, the 1851. The LO tube was changed from a 6J5 to a 6K6, affording higher
output in the VHF region. IF Gain controls were on the front panels of the prototype but
were eliminated for the production version. Also, the production DD-1 uses two IF amplifiers while the
early prototype had three. The meter arrangement is opposite of the
early prototype on the production model. The panels slope on the production version and a
transparent scale is placed over each tuning dial rather than the articulated
pointer.

The Production Skyrider Diversity DD-1

The new Diversity Receiver's advertising had been
carefully nurtured and the publicity was going to be more important to Hallicrafters'
reputation than any profits derived from sales of the receiver. Following their tradition of naming receivers, the DD-1 was
dubbed the "Skyrider Diversity" and the June 1938 issue of QST features no less
than 10 pages of ads devoted to the new receiver. All of the major component suppliers,
such as Mallory-Yaxley, Crowe, Aerovox, Jensen, Stancor, Aladdin and Raytheon weighed-in
with their own ads plugging themselves along with the DD-1. It was the largest ad campaign
for a new receiver up to that time and this was just QST! Advertising for the DD-1 was
everywhere.

The advertising campaign for the DD-1 didn't last very
long - only
about six months. Bill Halligan and probably everyone involved with the DD-1 project knew
that the Skyrider Diversity was not going to be a major seller. With prices between
$300.00 and $500.00, depending on options, the diversity receiver was just not in most
enthusiasts' budget. The base price for the receiver was to be $300.00, with the Power
Supply adding another $40.00 and the Audio Amplifier adding another $50.00. The Diversity
Action Meters sold for an extra $20.00 and the 12" Jensen table speaker sold for
$12.00. The total for the receiver with the standard accessories was $422.00. If the
purchaser wanted the ultimate, he could spend a full $500.00 for the Skyrider
Diversity Console DD-1. That price included the Diversity Action Meters installed in a matching
wooden top. The huge machine-age style speaker cabinet has shelves in the rear
(right side) to house the Power Supply and the Audio Amplifier. The 15" Jensen
Ortho-dynamic speaker is mounted in a Bass Reflex enclosure that takes up most
of the center and left side of the cabinet (as viewed from the front.) A small
table is provided as an arm rest for fine tuning the DD-1 or it could be used as
a small writing table for logs or whatever. The speaker has a 5000 ohm to 8 ohm
matching transformer mounted on it. The fabulous cabinet design was the work of
Auther Haggstrom, who had also designed cabinets for Jensen, E.H.Scott and
McMurdo Silver. When one looks for a price comparison to get a feel for what could be
purchased for $500 in 1938, look at the Chevrolet coupe, selling for $550 in 1938
- essentially, the Skyrider Diversity Console DD-1 was the price of a new car!
>>>

>>> Of
course, Hallicrafters realized they weren't going to sell very many DD-1
receivers. The price, the size and the usability was just not what the average ham could
justify. Hallicrafters
probably estimated that somewhere around 100 to 150* receivers would fill all of the orders
besides all of the publicity donations that might be needed. The major benefit to Hallicrafters
was to their reputation. They now had proven that they were
capable of successfully engineering and building a complex, dual-diversity receiver.

*For the past several years,
I have been collecting serial numbers of known DD-1 receivers in an effort to
estimate production accurately. It now (2014) seems likely that a production
quantity of 200 units is far too high. This estimate was originally based on
Halligan's 1980 statement regarding DD-1 production. It appears from the
reported serial numbers that an initial run was made that was somewhat less than
100 receivers and used serial numbers in the H-80500 to H-80600 range. A few
months later a very small production run was made, probably to use up the
remaining DD-1 parts inventory and this run accounted for a few receivers up to
maybe 40 or less receivers. Only three DD-1 receivers have
been reported with serial numbers in this later range, H-85617, H-85629 and
H-85648. The current
information leads me to believe that only about 120 DD-1 receivers were
produced and that total quantity came in two production runs of approximately 100 units and later
approximately 20
units.
See "Estimated DD-1 Production" section below for more details.

The DD-1 Advertising Images

This is an enlargement of the artwork that was used
for most of the DD-1 advertising by Hallicrafters. It is artwork - not a
photograph. Most advertising at the time used detailed drawings for
their images and though the Hallicrafters DD-1 artwork is detailed, it
is not a photograph. Whether it was based on an actual prototype or if
it was a "mock-up" is
not known but the receiver is different from the standard production
DD-1. Obvious is the lack of the Heterodyne Oscillator implying
that the BFO was a last-minute addition. Also, individual RF Gain controls on
the far right panel with a "Master RF Gain" control (large knob)
differs from the production DD-1. The tuning and BS dial logging scales
are different
and if there is any scaling on the tuning dial it is too light to see in
the finished artwork. The four smaller panels are plain with no decorative border.
Additionally, the toggle switches are mounted lower than center of the
panels while the production DD-1 has these switches mounted center of
the panel. The location of the larger knob on each lower panel is
different than the production units. The standard production DD-1 used
21 tubes in the receiver, four tubes in the Power Amplifier and one tube
in the Power Supply, bringing the total to 26 tubes.

photo above: Bill Halligan and some of the engineers with the DD-1. This is an actual photograph
showing a production DD-1. Although it is shown with the console
speaker, the wooden top with the Diversity Action meters is not
installed.

Both photos to the right also show production DD-1s.
Though all of the images are small it can be seen that the toggle switches are
centered in the smaller panels, the panels have a decorative border and the
knob arrangement is standard production. Also, the wooden top is installed
on the W6LYY DD-1.

More on photos right - The Skyrider Diversity Console DD-1 is shown in the shack of W6LYY,
Barney Boyd of San Diego, California. Boyd's shack was to be the state-side link for
communications to the Archbold New Guinea Expedition. The table version DD-1 that was delivered to New
Guinea for the Archbold Expedition. This set-up featured a special, 15" Jensen
speaker mounted in the familiar Hallicrafters speaker cabinet.

Photos - QST, Jan.1939

Restoration of
the Western Historic Radio Museum's DD-1

Before Restoration Photos and Assessment

DD-1 H-80596 was basically complete except for the top and bottom covers
for the Power Supply and missing interconnect cables. Minor condition
problems were present, mostly in the form of surface rust. The most
significant rust damage had occurred on the back of the power supply case
and the front of the power amplifier case. As for the receiver, some minor rust was present on the case mounting lips
but the most serious rust was located in the RF coil section of the chassis.
Most of the electrolytics had been replaced over the years, a coaxial cable
was installed to replace a shielded cable in Receiver B, the Master RF Gain
and Audio Gain controls had been replaced along with a handful of other
resistors and capacitors but the essentially the receiver was complete and
no modifications had be installed - just repairs. The plastic dial scales
were yellowed and warped - typical of
certain plastics at that time.

The finish on the wooden
top and on the speaker console was original. There were some small veneer
chips at the bottom of the console. The grille cloth was original. The 15"
Jensen speaker was original. There was obvious wear to the finish on each
side of the speaker console just below each of the control panel knobs
showing that the DD-1 was used extensively at one time. All wooden parts to
the cabinet were present including the rear cover.

The chassis photo was taken before restoration. The box-type shield cover has been
removed to show the Mallory-Yaxley Push-Button Band Switch assembly and the
associated coils. Note the brass threaded rod and nuts that runs through all
of the coil dividers. This, along with the shields, help support the
push button switch assembly. The round cans on each of the outer chassis are the
Infinite-Rejection tuning condensers while the rectangular cans are the
IF transformers. The large transformer on the center chassis in front is
for the tube heaters. One can see the three chassis that make up the construction of the
DD-1. Also, obvious are the spots of surface corrosion on the chassis and some components. This is
fairly typical of the cad-plated chassis of that time period. The most
serious rust was encountered at the rear-left of the RF shield box area. Not
only was the chassis involved but the shield also had a rust problem.

Photo
left: A
seldom seen sight,...two DD-1s on one workbench. In front is H-80596. To
the rear is a second receiver with many missing parts including the bandswitch
shield cover that had the SN tag attached to it.

Starting the Restoration

Initial Thoughts on the
Restoration - Before starting the restoration, I had to decide what
kind of job this was going to be. Of course, the end result was going to be a
fully functional DD-1, but was the DD-1 just going to be rebuilt with no regard
for originality? Or, was I going to attempt a restoration that resulted in the
receiver looking as if no parts had ever been changed and that it was in a "well
preserved" original condition that reflected its age. I opted for the latter
with some exceptions. First, since there was some significant rust damage on the
power supply and amplifier cases, they would have to be cleaned and repainted.
Also, since the top and bottom covers were missing from the power supply, new
reproductions would have to be fabricated using the covers from the amplifier as
models. All other cosmetic problems could be addressed by "touch-up." I prefer
my restorations to appear as if nothing has occurred. The finished receiver
looks its "age" but as if it was well taken care of and any rework that would
have happened would have been done professionally using original parts or parts
contemporary to the receiver's age. This requires that all paper-wax capacitors
be re-stuffed along with re-stuffing the electrolytic capacitors. This is a time
consuming process but it results in the under chassis appearing totally
original. With common receivers that were produced in fairly large quantities,
preserving original capacitor shells is not really worth the effort since there
are still many original examples existing. However, the DD-1 is another case,
since very few were built and fewer are still in existence, preserving the
originality was important.

Touch-up Painting
- The inside of the cabinet is matte black finish and was
touched up using artist's acrylic Mars Black mixed with a little water. I first
cleaned
any rusty areas with a wire brush and wiped the area with a cleaner - I used Glass Plus (no
ammonia.) When the area was dry I brush painted the black acrylic. The acrylic paint matches the matte finish very
closely. Artist's acrylic can also be used for small areas in the wrinkle finish
that are missing, such as scratches or scrapes. I don't thin the acrylic when
touching up wrinkle since the paint has some body and can be textured a little
with brush strokes.

For areas where about .5" to 2" were missing the
wrinkle finish I used Krylon Wrinkle Finish Black. I spray a small amount into a
small cup and then paint that on with a brush. Make sure the area to be touched up is
clean and has been wiped down with lacquer thinner. Paint a "heavy coat" on with
a brush and when finished apply heat using a 100W reflector lamp placed close to the
surface (about six inches away is good.) For trouble spots that are slow to wrinkle (more than 10 minutes) I use
a heat gun on low temperature to get the paint hot enough to start wrinkling and
then stop. Too much heat will cause the paint to "gloss" more than normal and
not match the rest of the original paint. Krylon's wrinkle finish paint is a
pretty good match for the color and texture - but nothing is perfect since the
original paint was a two part process requiring a nitrocellulose lacquer base
with a catalyst applied after the base was dry. The two part wrinkle then had to
be baked to activate the process. There were several different formulae that
resulted in the slightly different wrinkle patterns that we encounter today.

The chassis rust spots were wire brushed and then a brush-on
silver paint applied. This can be dulled to match the chassis with an acid brush
or similar mild abrasive. The transformer covers were touched up using this same
technique.

Power Supply and Power
Amplifier

Certainly the rust damage on the power supply
and power amplifier looks pretty bad. However, careful cleaning and rust
removal followed by a new wrinkle finish paint job and the two units
looked great. I did have to remove the damaged perf metal on the power
amp and replace it. When painted the new piece was undetectable from the
original.

All capacitors were re-stuffed in these units.
Luckily, all of the transformers in both units were original
and in good operable condition. In addition to the rebuild of these
units, two interconnect cables had to be made. I had some old battery
set, cloth covered cable that looked very close to the original brown
cables used by Hallicrafters. The AC connection is also via an
interconnect cable plugged into the rear of the receiver. This was a
rubber cable about 8 feet long. I installed a dual fused plug since the
DD-1 originally has no fuses on the AC line. Hallicrafters assigned the
amplifiers a
four digit serial number that is on a paper label on the bottom of the
unit.

The missing top and bottom covers for the power supply had to be
replicated at a local sheet metal shop. The shop used the original top and bottom covers from the power amplifier as models
since the covers are identical for both units.
It was a long wait for the completed parts as most shops consider this
type of work just for "fill in" unless you want to pay "full rate." I got
both covers made for $60 each. The top cover is an exact replica except the perf metal
holes are slightly smaller in diameter. The bottom cover is also an exact
replica except that it is made out of stainless steel so it wouldn't have to be
chromed.

When the top covers were painted wrinkle finish black, it was
difficult to tell which cover was the reproduction. The same for the
bottom cover when installed - only the original has a few rust pits that
show. The square rubber feet install on the two welded pieces that span
across the front and back corners.

Shown on the left are the finished Power Supply and Power
Amplifier. The Amp has its original top and bottom covers while the
Power Supply (on the right) has the reproduction top and bottom covers
installed. Although they can't be seen at this angle, the square rubber
feet are installed on both units. While the Power Supply and Power
Amplifier normally can't be seen with the DD-1 Console model, since they stow
on shelves located in the rear part of the DD-1 Speaker Console, it is
nice to finally have them both units complete and looking correct.

The first part of this project was to clean up all of
the rust problems. Most serious was an area in the 1st RF amp coil bay. This was
accessed by removal of all of the coil shielding. Naval Jelly and wire brushing
removed the rust and then the area was painted with a silver paint. When the
paint was dry it was dulled down to match the chassis color with an acid brush.
The same treatment was required on the tube shield section in addition to
installing two new mounting studs to replace rust damaged ones. Once everything
was clean and cosmetically restored the electronic part of the project was
started. >>>

>>> When working closely in the chassis many discrepancies
were noticed. These were checked either against the schematic or against the
second DD-1 chassis to help with the decision as
to what was correct. Also, as I proceeded through the circuit, I checked the
resistors for any out-of-tolerance conditions. I will usually allow about 30%
variation in the resistor values depending on their function.

DD-1 Receiver Electronic Restoration Details

Re-stuffing Paper-wax Capacitors

Since nearly all of the 49 paper-wax capacitors in my DD-1
were the original Aerovox caps, re-stuffing the old paper shells with new
capacitors was a practical idea that would result in an original under chassis
appearance. One potential problem with any serious rework of the DD-1 is the
polystyrene tube sockets. These sockets will not tolerate any over heating and
therefore desoldering should be avoided. It is possible to use "hook" splices
for joints and if carefully done and kept very short they will not be apparent. This
avoids overheating damage to the plastic sockets and to other components.

Since I was re-stuffing original shells I had to use
"yellow-jacket" type, film capacitors. To re-stuff a paper-wax capacitor I use a heat gun to melt the old end seals on the original
capacitor. Some caps will almost fall out of the shell when hot but not Aerovox
caps. I had to use two needle-nose pliers on each wire lead end and pull the cap
apart to remove it from the paper shell. While the shell is still hot from the
heat gun I wipe the shell off with a paper towel to clean it up. The new cap is
then inserted inside the old shell. I orient the new caps all the same way - it
doesn't really matter with film type caps but it is just habit to do so. The new
cap is held in place with hot-melt glue. When the glue has set-up, I fill the ends with brown sealing wax. The
resulting capacitor is new inside and appears to be the original since we are
using the old paper shell. It takes about 10 minutes to re-stuff each capacitor.
Be sure to install the re-stuffed cap in the correct orientation - this is for
appearance only. Also, there was a .01uf capacitor
inside the BFO can that needed to be re-stuffed.

Photo: The completed under chassis restoration showing
the re-stuffed paper-wax capacitors and re-stuffed electrolytic
capacitors. The orange electrolytics
are Beaver brand and are original shells. These caps were engineering upgrades
in production that are not shown on the schematic. The end
result of this restoration method is a fully functional DD-1 - plus, a
reference that shows how the DD-1 looked as it came from the factory.

When the tedious part of the restoration was completed I
then needed to install a complete set of tested tubes. Each tube socket is
cleaned and when the tube is installed a small quantity of De-Oxit is sprayed on
the tube pins and the tube is plugged in and out of the socket a few times
before final installation. Usually during the rebuild process the pots and
switches are cleaned with De-Oxit. After this process, the DD-1 was ready for
power-up. There are always going to be a few minor troubleshooting problems after initial
power-up and the DD-1
was no exception. Fortunately, the DD-1 did basically function and only had some
minor problems that needed to be sorted out before it could be aligned. >>>

>>> Having another DD-1 chassis to look at for reference was
a tremendous help. Not only could suspicious parts be checked for originality
but missing parts could be referenced along with wiring and component placement
checked. It took about one week to complete the paper-wax capacitor re-stuffing
part of the job. Though tedious, I think the underside of the chassis looks
great now and it is almost impossible to tell that any capacitor has been
replaced. A few resistors were out of spec or were old repairs where wrong
values were installed or repairs where an incorrect style (like JAN type) was
installed. These were all replaced with correct values and correct styles, again
to preserve as much original appearance as possible. Below are all of the major
problems encountered.

Non-Original Parts

Metal can electrolytic capacitors installed for 8 mfd screen
filter caps. These had mounting clips that were soldered to the chassis. The
clips were removed as was the solder residue and the correct value, style and
brand (Beaver) rebuilt electrolytics were installed.

Coax cable connecting Receiver B Mixer to Receiver B IF amp.
I installed new coax with tinned copper shield and removed the outer jacket so that the appearance was
the same as original.

Master RF Gain control was defective and non-original.
Replaced with correct style and value part.

Audio
Gain control replacement part that was wrong value and style. Installed correct
style and value part.

The DD-1 schematic and parts list contain several errors.
This was probably due to the receiver's short production life. Hallicrafters
would normally correct the documentation with the second issue of the manual or
perhaps with an errata sheet. Since the DD-1 was only in production for a few
months and only a hundred or so were built, when production halted, apparently
everything else involved with the receiver also stopped. This included all
updates to the flawed schematic and documentation of any engineering upgrades
that were incorporated into the production units. Fortunately, most of the
errors are not critical to repairing or restoring the DD-1 receivers. Some of
the conflicts are actually engineering improvements and these should be left
installed. Since I had two DD-1 receivers at the same time, I was able to
compare the schematic to production conflicts and resolve what was correct for
the receiver. Additionally, I had two other resources in fellow DD-1 restorers
who were able to confirm that their receivers also
had similar production upgrades. The following is a list of schematic errors and
non-documented engineering upgrades to the DD-1 receiver.

Schematic vs Engineering Upgrades

Two 8 mfd electrolytic capacitors on the 250vdc B+ line
for RCVR A & B on each 1st IF AMP tube screens - provides better filtering of the screen supply. Non-documented upgrade.

One .01ufd paper capacitor installed on plate to cathode
of 6J5 Heterotone Oscillator not identified on schematic. Schematic error

Input IF transformer T-1 on Rcvr A and B has trimmer on
secondary only - schematic shows T-1 is with both primary and secondary
trimmers.

Output IF transformer T-3 on Rcvr A & B has two trimmers
- schematic shows T-3 with one trimmer. Schematic error in both cases.

Alignment instructions do not address the PHASE
adjustments on the IF A and B chassis. This was thought to be a one time
adjustment carried out at the factory but over time certainly someone probably
moved the adjustments to see what happened. Instructions for proper adjustment
are in November 1937 QST in an article on the Infinite Rejection IF by Karl
Miles and James McLaughlin. The PHASE adjustments control the power factor on
the IF transformers and therefore the depth of the rejection notch. Alignment
instructions over-sight.

Several variations on values of resistors encountered -
this was probably due to production supply, e.g. 20K on schematic parts list is
actually 25K in receiver.

Diversity Meter B initially seems to be wired reverse
but this is correct for the way the meters work mechanically. Div Meter A + is +
and Div Meter B + is -

Bass Reflex Cabinet

The Machine Age styled cabinet was designed by
Auther Haggstrom and features the Jensen
Ortho-dynamic 15" High Fidelity speaker with bass reflex port. The
cabinet also allows stowage of the power amplifier and power supply on
the two shelves. The cabinet is in excellent original condition with
original grille cloth and all of the various wooden covers intact. The
finish is in good condition with some wear apparent, including the
ubiquitous "water glass ring." This just allows the cabinet to "show its
age." One can also infer from these wear marks that a former owner
enjoyed this DD-1 for several years, spending many hours tuning in
various shortwave broadcasts from around the world.

The photos below show the rear of the cabinet with
the back installed and with the back removed showing the 15" Jensen. The
PS and Amp are shown in place but without their covers or bases

IF/RF Alignment of
the DD-1

The most
important part of any rebuild is the alignment. Changing all of
the caps is important but alignment is what makes the receiver
perform like it did when it was new. The DD-1 is straight
forward in its alignment - just that there are two separate
receivers so there are twice the adjustments that need to be
made. The only tedious part of the alignment is the
Infinite-Rejection tuning. If the PHASE adjustments have not
been tampered with you can follow the alignment instructions.
They are confusing since the instructions first state that two
signal generators are necessary and then proceed along the
assumption that you only have one generator. If the null seems
flat or non-existent then the PHASE adjustments need to be
changed, however the alignment instructions assume that the
PHASE adjustments are at the factory settings. The PHASE
adjustments control the IF transformer power factor and
therefore the depth of the null. >>>

>>> More details on
the PHASE adjustments are in the December 1937 QST article on the
Infinite-Rejection IF system. Above 15MC it is possible to align to an image.
Keeping the RF generator signal level low will reduce the image to an extremely
low level. Also, I usually check WWV frequency location and any image location
to be sure the tracking is correct. The top band is will align fine but it is
not very sensitive. Additionally, there is not very much activity in that part
of the spectrum for checks.

Looking inside the chassis area of the finished DD-1 with the
box-type metal shield installed. The serial number tag is riveted to this shield on the right-side towards the rear of the chassis.
All of the shields and screws must be installed along with the threaded
rod and nuts that secure each metal divider. This is mechanical strengthening
for the Yaxley push button switch to keep it aligned for reliable
operation.

Note the reproduction plastic
scales over the tuning dial and the bandspread dial. These were made by
K6DGH.

Also note the brown plastic handles on the switch levers. All DD-1
receivers had lever handles that are similar to the black band switch
push-button knobs (except they are not recessed for the band indicator
ID.) The brown lever handles were installed on my DD-1 when I got it.
They are almost certainly not original (but they are vintage, look really nice and they do all match.)

Performance of the Restored DD-1

To say that the DD-1 is an impressive looking receiver is
certainly an understatement. Its size alone allows this receiver to dominate the
room it is in. However, does its performance match its appearance? First let's
cover our receiving set-up. Ideally, for space diversity the antennas should be
separated by at least a wavelength at the receive frequency. The Hallicrafters
DD-1 manual makes
a point to say that a "useful" diversity effect will be noticed even if this
separation cannot be achieved. This is true. Our set-up consisted of several
different configurations. First I used an end-fed wire 40 feet long on Rcvr A
and the metal framework for a suspended ceiling for the antenna for Rcvr B.
Surprisingly, this did give a noticeable diversity affect above 15MC. Also tried was one
leg of a 135 ft. center-fed Zepp and the 40 ft. end-fed wire. This combination
gave useful diversity effect down to 75 Meters even though the separation was minimal.
Obviously, the recommendation of one wavelength separation is for continuous
maximum diversity effect.

Sensitivity is typical for a late thirties receiver, in other
words, don't expect too much performance above 25 MC. The 1851 RF amp tubes are
supposed to be operable up into VHF but the coil losses, band switch losses and
wiring losses all add up to a marked decrease in sensitivity above 25 MC.
Though images can been found when aligning (if the RF generator level is too
high) they are not apparent when tuning any of the higher frequency Shortwave
bands. Selectivity is wide open with no adjustability. The design used
Infinite-Rejection tuning for heterodyne relief. This circuit features a tunable
notch that can be moved around the passband and thus reduce or eliminate
bothersome heterodyne interference. Nowadays, heterodynes are rarely encountered
so the I-R Tuning doesn't really find much use.

One thing should be realized, the DD-1 is
really not a CW receiver. Diversity is difficult in CW as a standard BFO
captures the detector and renders the AVC non-functional. The DD-1 uses a
Heterotone Oscillator to modulate the wave envelope at the last IF stage and
provide a modulated CW signal. This
does work fairly well but requires a strong CW signal with no QRM to give good copy.
Also, the AVC is on when using the Heterotone Osc. so the RF gain should be kept
fully advanced to take advantage of any diversity effect. It is disconcerting to
hear a constant 500 Hz or 1000 Hz tone
while tuning around the band and then as you tune through a CW signal to have
that tone suddenly break into readable CW. But it is sudden,...one can sort
of hear the CW signal behind the Heterotone oscillator and when the signal is
tuned perfectly centered in the passband, you suddenly hear what sounds like
a MCW signal (modulated CW.)
By reducing the Master RF Gain slightly the constant tone is reduced while
"tuning around" but this does reduce the sensitivity and can reduce the diversity effect. Since the Heterotone required strong signals and prevented hearing the weaker CW signals
when tuning around, it just wasn't going to work for hams who were CW
enthusiasts. Hence, the Heterodyne
Oscillator or standard BFO. >>>

>>> For the CW operator, either Rcvr A or B can be
used individually with the BFO. In this set-up you have to operate the DD-1 just
like a standard receiver - back the RF gain down and advance the AF gain - AVC
is automatically turned off when the BFO is on. Use the RF gain to control the signal level to the detector for
the proper ratio of signal to BFO injection. The BFO seems
to have a very wide range and only a slight movement of the knob has the BFO
frequency plus or minus several hundred Hz. The Heterodyne Oscillator also
allows SSB to be copied with no problems but you do have to "ride" the RF gain
for good copy. Using the Heterotone Oscillator for SSB doesn't work at all.

How does it perform on AM Ham signals? The DD-1 provides
excellent audio and performance on almost all Ham AM signals. Tuning into the
West Coast AMI net results in nearly all stations being heard and the high
quality AM stations sound incredible on the DD-1. Fading is not really
noticeable however watching the Diversity Action Meters will show that the
signal at either Rcvr A or Rcvr B is always changing strength and that the DD-1
S-meter (on the AVC line) is holding steady, at least most of time. The
diversity action is especially noticeable when rapid QSB is happening on one
antenna only. How about Shortwave Broadcast? Here is where the
DD-1 should be at its best because it is dealing with strong AM signals that are always
fading and the listener can
take full advantage of the diversity affect. Unfortunately, the higher frequency
SW BC stations seem to fade equally on each antenna. Sometimes a diversity
action will be noted but equal fading is the norm. With better
antenna separation, the diversity action on SW BC should become more
consistent.

Audio quality is great and there is ample power with the
P-P 2A3 audio tubes - 10 watts according to the manual. AM BC stations that are
broadcasting music sound very nice with very deep bass and ample highs - too bad
there are so few AM stations broadcasting good music. SWBC stations also sound
really nice, especially when they aren't fading all of the time.

So, was the DD-1 a great receiver? From an engineering and
design stand-point, it certainly was. It does exactly what it was supposed to
do, reduce or eliminate fading radio signals and provide great audio for
pleasurable listening. From an industrial arts point of view, the cabinet design
is striking and imposing - a focal-point of any room that it would be placed
into. As a practical, useable ham receiver? Probably not,
especially considering the high selling price. Without a doubt, the average 1938 ham would
have been much happier with a National HRO Senior or a Hammarlund Super-Pro at
half the cost. The awkward way that CW has to be received would have
disappointed most ham users and CW accounted for a very large percentage of the
ham operators in 1938. There were avid AM Phone operators in 1938 and certainly
the DD-1 would have been great for that, if it was affordable. The wealthy SWL would also have been
thrilled with the DD-1 performance.

Nearly all DD-1 serial numbers encountered so far are in the
H-805XX range. One might infer from a single DD-1 serial number that
perhaps more than 500 receivers were produced with the numbers starting at
H-80,000. However, Hallicrafters assigned serial numbers sequentially as
products left the production line and exclusive number blocks were not used or
ever assigned to specific models. Therefore, serial numbers alone cannot provide
the information necessary to determine an exact number of DD-1s produced. One
can estimate a number based on the known examples (and perhaps include the small
quantity that has appeared on eBay over the last several years.) That number is
very small indeed, with around two dozen examples, including the few
DD-1s that have been offered for sale. This leads one to conclude that the total number of DD-1
receivers produced was certainly far less than the "200" that Bill Halligan
"recalled" that had been manufactured. Of course, the interview with
Halligan was decades later but he always did seem
to exaggerate some of the production figures, e.g., Halligan claimed 50,000
SX-28 receivers produced when a more accurate estimate is 28,000. As far as any archival records, when Hallicrafters was sold to Wilcox Instruments
(aka Wilcox Electric,) a Division
of Northrop, in the early 1970s, all of the production records along with all of Hallicrafters archives were destroyed by orders from Wilcox Instruments!
Another identification problem is the location of the DD-1 serial number tag. Since
it is riveted to the bandswitch-coil shield-cover, if this shield is missing so
is the serial number. This was a problem found on two of the four DD-1s I have
inspected. Also, the two out of the three "unknown" DD-1 serial numbers in the log are due to
missing original shield boxes.

DD-1 Serial Number Tag
Location

The Serial Number Tag is located on the right
side of the coil-bandswitch shield box. The tag is riveted to
shield box towards the rear. With the top removed the tag is
easily visible as shown in the photo to the left. Details of the
tag are shown in the photo to the right. Absence of a serial
number tag generally indicates that the shield box is a
reproduction.

So far, 22 serial numbers assigned to DD-1
receivers have been reported. The numbers range from a low of H-80510 to
a high of H-85648. All numbers but three are in the H-805XX range. The
exceptions are H-85617, H-85629 and H-85648. Dates of the assignment of close numbers
reported from inspection tags reveal that H-83879 was assigned on
November 11, 1938. Serial number H-85531 was assigned on December
19,1938. Only 86 numbers separate this last serial number from DD-1
H-85617, which dates that DD-1 serial number assignment to the week of
December 19, 1938. Since the DD-1 was announced in June, 1938 one would
assume that they were available at that time, however this was rarely
the case with new product introduction. Most likely, the range H-805XX
was assigned during September, 1938. At this time, Hallicrafters was
assigning about 425 serial numbers per week. One can infer several of
things from the serial numbers reported so far. First, the production
quantity of DD-1 receivers was very small. Second, that there was two production runs for the DD-1, one in August-September 1938 and
one in December 1938 - January 1939. >>>

>>> Also, it is possible that
all of the DD-1 receivers built for the first production run were
completed at approximately the same time and serialized sequentially. It
is highly unlikely that a specific block of "H-805xx" serial numbers
were assigned to the first production run DD-1 receivers. More than
likely the first DD-1 is serialized somewhere near H-80500 or so. The
lowest reported serial number is H-80510 and the highest reported first
production run serial number is H-80596. If all serial numbers within
the known sequence were assigned to DD-1s, the total would be around 86
receivers. It is likely that the second production run was a very small
quantity since only three serial numbers from that period has been
reported. It is likely that only what was necessary to use up the parts
inventory accounted for the second run. Possibly the first run was for
80 to 100 receivers while the second run was for anywhere from just a
few receivers to perhaps 30 or 40 receivers. This brings the total
estimated production to a possible low of maybe 85 receivers to a high
of perhaps 140 receivers. An average estimate that seems reasonable is
that around 120 DD-1s
were produced. This is just speculation based on what has been
reported so far. More serial number
examples will provide better picture of the DD-1 production history.

DD-1 Serial Number Log

Known DD-1 Serial
Numbers (listed sequentially) and Current Owners (listed by amateur call sign,
if applicable)

Tom, WA2LTD, owns the earliest serial number DD-1
reported so far. It is a console model although the photo is only of the
receiver. Tom has all of the components to this DD-1 including the power
supply, audio amplifier, speaker console and the diversity action meters
installed in the wooden top cover.

Note the black knobs on the switch levers - this is the
standard knob usually found on DD-1 receivers.

WA6CJT - H-80519

Here is a photo of DD-1 sn H-80519.
Frank has recently acquired this excellent receiver from well-known Hallicrafters collector, Chuck Dachis.
Note the color-coded buttons on the band switch. More information to come.

UEC Museum - Tokyo, Japan -
H-80520

DD-1 H-80520 is a table model set that is now located
in the UEC Museum in Tokyo, Japan. Originally owned by JA1BHR, Mr.
Yasuda, the DD-1 was donated to UEC after JA1BHR became SK. The
photograph to the left is shows JA1BHR on the cover of a Japanese ham
magazine from 1975. Note the DD-1 upper right behind the globe. The
magazine is part of the DD-1 display at UEC. Thanks to Hiroshi Ogawa
from Tokyo for providing the information on the DD-1 and the photograph.
Also, thanks to Skip Magnuson W7WGM for contacting both Electric Radio
and Hiroshi Ogawa to obtain this DD-1 serial number.

K6DGH - H-80521

Peter has owned this console DD-1 for many years. He
fully restored H-80521 about ten years ago. His
restoration involved replacement of all resistors and all capacitors.
Additionally, he repaired or replaced several of the IF transformers. A
total rebuild of the Yaxley push button band switch assembly was also
needed. The wooden top piece and speaker console were refinished along
with replacement of the grille cloth. The metal plating and the black
wrinkle finish is original.

photo
by: K6DGH

Frank Adams - SN: H-80534

Here is a photo of the DD-1, SN H-80534 owned by Frank Adams. This is the
table top configuration with the power supply and amplifier flanking the
DD-1 receiver. Also included are the optional Diversity Action Meters
housed in the small cabinet to the right of the speaker. The speaker is homemade and contains a 12" speaker. This
DD-1 was formerly owned by Skip Magnuson who did all of the rework to
make it an operational DD-1 (all of the electrolytic capacitors
replaced and some other minor repairs.) Skip sold his DD-1 to collector
Frank Adams in October, 2016.

(photo by W7WGM)

W5CZ - SN:
H-80584

For the past 50 years, Benito Serrano was the
owner of this DD-1 receiver. The receiver was located in Bogata,
Colombia and owned by Benito's granddaughter, Diana. The DD-1 was
recently purchased by Rod Perala, W5CZ who has fully restored it and is
currently using it with an RCA ATC-40 transmitter "on the air." New
photos coming soon.

WB5KLJ - SN: H-80589

This table top DD-1 is owned by Ron WB5KLJ of
Goldfield, Nevada. It worked the last time Ron powered it up but that
was several years ago. Ron is planning on starting the restoration of
his DD-1 soon, so updates may be coming.

WA7YBS - SN: H-80596

This is the highest known serial number DD-1 from the
first production run. We displayed this DD-1 at our Western Historic Radio Museum
in Virginia City, Nevada from 2002 up to the closing of WHRM to the
public in 2012. It is shown in the photograph left at our new QTH
in Dayton, Nevada. We've located the DD-1 in the upstairs landing-nook
where it is the first receiver encountered when entering the
"Communications" section of the house.

WB9YIR - H-85629

This is a
second production run DD-1. This receiver had spent some time in Europe
where the original power transformer (a 115vac primary) was replaced
with a transformer with a 240vac primary. Gary is in the process of
restoring the PS for this DD-1 back to the original configuration to
operate on 115vac. The receiver itself is in superb condition although
some of the capacitors were replaced with modern components. Again, Gary
is going to be returning the receiver back to an original under the
chassis appearance as part of his restoration.

NU6AM - SN: Unknown

This is the restored DD-1 belonging to NU6AM. The receiver is
completely rebuilt and functions quite well. Jim has used his DD-1 on
several AM QSOs on the 80 meter band. The cabinet is restored as is the top. Interestingly, "SKYRIDER"
is actually engraved as "SKYR DER" - the "I" was skipped although the
space is there. Probably the engraver had set up the panagraph machine
with the correct letter dies but skipped the "I" when performing the
actual engraving which results in the correct space but no letter. Also,
interesting that this panel made it through Hallicrafters' inspection
process. This DD-1 was missing the original box shield and therefore the
serial number is unknown. A reproduction of the shield was made and
installed.

Conclusion and On-going Research

The DD-1 was to remain unique in receiver
manufacturing as the only example of dual diversity circuitry designed
for the ham market. Its lack of success was due to many factors that
Hallicrafters should have anticipated - maybe they did and decided that
the success was to their reputation and that was more valuable than
profitable sales of the DD-1.

DD-1 survival rates seem to
be much better than the average ham receiver or AM BC radio. This is
expected since the selling price was nearly that of a new car and many
of the original owners cherished their purchases for their entire lives.
On the average, ten percent survival of total production is considered
normal. I think the DD-1 is going to at least double that survival rate
due to its uniqueness and the original expense of purchase

I have only been able to
examine four DD-1 receivers in detail. 22 serial numbers
have been collected so far. As with my article on the Hallicrafters SX-28, the
information in this DD-1 article is always being updated to reflect new
data that is supplied by Hallicrafters enthusiasts, collectors and
interested hams. We need more serial numbers to more accurately estimate
total quantity and the length of time the DD-1 was in production. Dated
inspection tags are a great help as these tie the serial number to an
exact production date. These are paper-wire tags that are usually
attached to the line cord of each receiver. These tags sometimes have
survived but I have never heard of one being found with a DD-1. Any
dated tags that are in the SN H-80,000 to 86,000 range would help with
more exact dating, regardless of what model the receiver it is.

If you have a DD-1 that has some differences from what I have listed in
this article, please let me know. These variations (especially when tied
to a serial number) can trace the engineering evolution or production upgrades of the DD-1. I will add these to the article for reference. Also,
operational DD-1 performance appraisals would be
interesting and would be included in this article if submitted (credit
will be given.) E-mail me a photo of your DD-1, I'll add it to the DD-1
photo gallery.

Since all of the Hallicrafters
archives and files were destroyed in the 1970s, collectors and
enthusiasts now have to share our information in order to help renew our knowledge of
this period of time in Hallicrafters' manufacturing history.

1. QST May 1936, QST December 1937, QST June 1938, QST January
1939, QST March 1939 - all have articles or ads about diversity or the DD-1

2. Radio News, August 1933 - Diversity Reception by Murray G.
Crosby - great article about H.H. Beverage and H.O. Peterson and the diversity station at
Riverhead, NY. Murray Crosby worked for Harold Beverage at RCA.

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